The invention relates to improvements in the operation of slide gate nozzles in their application to metallurgical vessels in particular to ladles and the like for liquid steel.
When such ladles are refilled with liquid steel their walls are inevitably at a considerably lower temperature than the melting point of steel. This is particularly the case in the narrow exit channel leading from the bottom of the ladle to the closed sliding plate of the slide gate nozzle. For design reasons this channel can neither be shortened nor widened at will. In consequence the liquid steel pouring into this channel inevitably freezes, so that the slide gate becomes inoperative, i.e. does not allow steel to pass through in the open position.
The universal remedy for this drawback is the introduction of oxygen into this channel which ignites the large lump of frozen but still very hot steel so that the exothermic reaction thaws the blocked passage. Though effective, this method is very undesirable and not without danger.
Other methods have been proposed but none without other drawbacks and/or with lasting success. Among them is the filling of the exit channel with refractory material of a suitable grain size prior to refilling the ladle itself. This prevents the steel from entering the channel prior to teeming. Even when the method works satisfactorily it has the drawback of allowing this refractory material to drain into the mold which is in many cases highly undesirable.